Pump wear plate viscometer

ABSTRACT

A modification of a spinning pump wear plate that enables it to be used both as a means to distribute polymer to spinning units and as an apparatus for monitoring melt viscosity of the polymer. The modification is such that polymer supplied through the wear plate by the spinning pump is first forced through a strainer, then through an orifice with a pressure transducer on each side of the orifice to measure the pressure drop across the orifice. A thermocouple or other temperature measuring device is positioned in the polymer stream near the orifice.

te it] States Patent 91 ,ioes, Jr.

[ 1 Feb. 27, 1973 [54] PUMP WEAR PLATE VISCOMETER [75] Inventor: Thurman Ralston Jones, Jr., Greenville, N.C.

[73] Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

[22] Filed: Feb. 16, 1971 [21] Appl. No.: 115,657

[52] US. Cl. ..425/l46, 425/382, 264/40 [51] Int. Cl. ..B29f 3/06 [58] Field of Search ..425/l70, 199, 198, 382, 145, 425/146; 73/55; 264/40 [56] References Cited UNITED STATES PATENTS 3,375,704 4/1968 Thompson et al ..73/55 2,696,636 12/1954 McDermott ..425/ 197 3,138,950 6/1964 Welty et al ..73/55 3,524,221 8/1970 Jones ..425/ l 70 Foust et al ..73/55 OTHER PUBLICATIONS Product Licensing Index, Page 23, July 1970.

Primary Examiner-J. Spencer Overholser Assistant Examiner-Michael 0. Sutton Attorney-Howard P. West, Jr.

[5 7] ABSTRACT A modification of a spinning pump wear plate that enables it to be used both as a means to distribute polymer to spinning units and as an apparatus for monitoring melt viscosity of the polymer. The modification is such that polymer supplied through the wear plate by the spinning pump is first forced through a strainer, then through an orifice with a pressure transducer on each side of the orifice to measure the pressure drop across the orifice. A thermocouple or other temperature measuring device is positioned in the polymer stream near the orifice.

1 Claim, 3 Drawing Figures PATENTEDFEBZHSH.

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ATTORNEY 1 roll/ii WEAR PLATE VISCOMETER BACKGROUND OF THE INVENTION This invention is concerned with the manufacture of synthetic fibers and, more particularly, with monitoring the melt viscosity of a thermoplastic polymer as it is melt spun into a synthetic yarn. Viscosity changes in the polymer can be used to calculate and make appropriate corrections in the polymer finisher conditions. Even when the polymer may be within predetermined, acceptable limits for commercial production, corrections in the conditions can be made once a trend in viscosity is evident, thus bringing this property back toward midrange and avoiding off-specification production.

The preparation of synthetic fibers from thermoplastic polymers, such as polyesters and polyamides, is well known. The desirability of a high degree of uniformity in synthetic yarns is well recognized and, for this reason, great efforts to obtain uniformity are made in commercial manufacturing processes. A basic requirement for uniform synthetic yarns is a uniform and homogeneous polymer supply, particularly with respect to polymer molecular weight. Many methods of measuring polymer molecular weight are known and used to monitorand control the reactor or finisher conditions utilized in polymer preparation and the spinning conditions. The known method of monitoring polymer melt viscosity described by Jones in U.S. Pat. No. 3,524,221, issued Aug. '18, 1970, utilizes a pressure transducer fitted into a spinneret in such manner that the transducer measures the polymer pressure immediately above the spinneret and thereby gives an indication of the pressure drop across the spinneret capillaries. While this apparatus arrangement has proven extremely useful in the manufacture of synthetic filaments, the location of the pressure transducer interferes with quick changes of spinnerets, and any change in the number of spinneret holes requires recalibration of the equipment.

It is known to use a wear plate or an adapter plate for mounting spinning pumps on spinning machine blocks. One method of constructing such wear plates is described by Bayer et al. in U.S. Pat. No. 3,050,846. The present invention involves the modification of a spinning pump wear plate that enables it to function both as a means to distribute polymer to spinning units and as an apparatus for monitoring melt viscosity of the polymer.

SUMMARY OF THE INVENTION The present invention provides an apparatus for monitoring the melt viscosity of a thermoplastic polymer as it is melt spun into yarn. The apparatus is both simple and sturdy, is easily installed, is close to the spinneret but does not interfere with spinneret changes and has been found to be a sensitive and effective monitoring instrument.

The apparatus of the invention, in its simplest form, consists of a modification of a spinning pump wear plate. The apparatus includes a source of molten polymer connected to a wear plate through which polymer is distributed from the source to a plurality of spinning units by means of a metering pump connected to first and second passages in the wear plate leading from the source to the pump and from the pump to the spinning units, respectively. The improvement comprises a strainer positioned upstream of a restricting orifice placed in the second passage; a pair of pressure transducers positioned in the second stream, one immediately upstream and the other immediately downstream of the orifice and a temperature sensing element positioned in the second passage adjacent the orifice. The apparatus is so designed that polymer supplied by the spinning pump, prior to entering the spinning pack assembly, is forced through the strainer and then through the orifice, with the pressure transducers measuring the pressure drop across the orifice. The temperature measuring device is inserted in the polymer stream near the orifice in order to provide a reading of the actual temperature of the polymer as it traverses the orifice. The pressure and temperature signals are amplified and recorded by conventional commercial amplifiers and recorders. If desired, the signals may be fed into an integrator and controller which, in turn, controls a regulator for the polymer making apparatus which supplies polymer to the spinning machine.

It is well known that melt viscosity is related to the ratio of shear stress to shear rate. In the present invention, polymer is metered through the measuring orifice at a constant flow rate, which provides a constant shear rate. At constant shear rate and constant temperature, melt viscosity then becomes directly related to shear stress, which, in turn, is directly related to the pressure drop through the viscosity measuring orifice. Thus, under steady-state conditions, the pressure drop provides a direct indication of melt viscosity.

Because melt viscosity is temperature and pressure dependent, it is necessary to continuously measure and record the temperature and pressure of the polymer movingthrough the orifice and apply suitable correction factors for temperature and pressure fluctuations, as needed. These corrections may be carried out automatically by readily available computer elements, or by other standard control devices.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic, perspective drawing of ap paratus useful in practicing the invention.

FIG. 2 is a side elevation view, partially cut away, of a spinning pump wear plate modified in accordance with the invention and showing the spinning pump in place. I

FIG. 3 is a top view, partially cut away, of the apparatus of FIG. 2, with the spinning pump removed.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT In the drawings, molten polymer from polymer finisher l is passed to screw pump' 2 which forwards the polymer through heated transfer line 3 to a spinning position where the polymer enters spinning pump wear plate 4. The polymer moves through the entry channel 5 of the wear plate to spinning pump 6 which is a gear pump of the general type described by Heckert in U.S. Pat. No. 2,281,767. From the pump, the polymer traverses channel 7 of the wear plate to strainer 8 which removes particles which might obstruct the viscosity measuring orifice. From strainer 8, the molten polymer moves through channel 9, past 1 pressure sensing element 10, through orifice 11 and then past the second pressure sensing element 12. The molten polymer then continues through channel 13 to the tip of the thermocouple 14 where the channel is subdivided into multiple channels 15 which feed the molten polymer to several different spinning units housed in spinning machine block 16. The spinning units housed in spinning machine block 16 are conventional filterpack-and-spinneret assemblies from which filaments 17 are extruded and quenched in chamber 18. The filaments are wound up in package 19.

The signals from pressure transducers l and 12 and thermocouple 14 are transmitted to amplifier-recorder 20 for read-out. If desired, the signals may be further processed by integrator-controller 21 and a control signal fed to polymer finisher regulator 22.

Strainer 8 may be any one of a number of suitable designs. The illustrated embodiment shows a cylindrical screen mounted in a quick change compartment with the direction of polymer flow being from outside the screen cylinder towards the inside. Other arrangements are equally suitable. A 50-mesh stainless steel screen has been found satisfactory for many situations.

Viscosity measuring orifice 11 may contain a single hole or several holes, depending upon the rate of polymer flow and the shear stress desired. For some purposes, a shear rate of 3,600 see. is satisfactory. In operating one embodiment of the invention where the polymer was polyethylene terephthalate having an intrinsic viscosity in the range 0.4 0.6 and throughput was 80 pounds per hour, a suitable orifice consisted of 6 parallel capillaries, each having a diameter of 0.062 inch and a length of 0.062 inch.

Pressure sensing elements and 12 may be any suitable device of sufficient sensitivity which is stable at the temperature of operation. A suitable device is the Dynisco Melt Pressure Transducer Model PT-422, available from the Dynisco Division of American Brake Shoe, 40 Ames Street, Cambridge, Massachusetts. This device uses a bonded strain gauge measuring element for converting pressure indications to electrical signals.

In FIGS. 2 and 3, separate parts of the apparatus are placed together in sealing relationship by means of suitable 0" rings 23. Other types of suitable gasketing arrangements may be used, if desired.

If desired, a third pressure transducer may be installed at location 25 in FIG. 3. By measuring the difference in pressure between location 18 and the pressure recorded by transducer 10, the pressure drop across filter 8 may be monitored and the filter removed for cleaning when the pressure drop becomes excessive.

What is claimed is:

I. In a melt spinning apparatus that includes a source of molten polymer connected to a wear plate through which polymer is distributed from the source to a plurality of spinning units by means of a metering pump connected to first and second passages in the wear plate leading from the source to the pump and from the pump to the spinning units, respectively, the improvement comprising: said second passage having a restricting orifice, a strainer positioned in said second passage upstream of said orifice; a pair of pressure transducers positioned in said second passage, one immediately upstream and the other immediatel downstream of said orifice; a temperature sensing e ement positioned in said second passage adjacent said orifice; and another pressure transducer located in said second passage upstream of said strainer. 

1. In a melt spinning apparatus that includes a source of molten polymer connected to a wear plate through which polymer is distributed from the source to a plurality of spinning units by means of a metering pump connected to first and second passages in the wear plate leading from the source to the pump and from the pump to the spinning units, respectively, the improvement comprising: said second passage having a restricting orifice, a strainer positioned in said second passage upstream of said orifice; a pair of pressure transducers positioned in said second passage, one immediately upstream and the other immediately downstream of said orifice; a temperature sensing element positioned in said second passage adjacent said orifice; and another pressure transducer located in said second passage upstream of said strainer. 